In W-CDMA (Wideband Code Division Multiple Access), which is a third-generation mobile communications system, a mobile station (UE: user equipment) in a CELL_FACH (Forward Access Channel) state has no specific base station to which it is subordinate, and selects a base station each time the mobile station transmits control information or the like. The operation of RACH (Random Access Channel), which is an uplink data channel, is stipulated in a specification of the standardization project, 3GPP (3rd Generation Partnership Project), for third-generation mobile communications systems (see Non-patent Documents 1 through 4, for example). Moreover, in 3GPP Release 8, a technique for enhancing RACH, E-RACH (Enhanced RACH), is being studied (see Non-patent Document 5, for example). An operation of E-RACH will be briefly described with reference to FIGS. 1 through 3 hereinbelow.
FIG. 1 is a block diagram showing a configuration of a mobile communications system. For preventing complexity of explanation here, it is assumed that a plurality of mobile stations 20-1, 20-2, 20-3, . . . , 20-N are located in a cell 40 of a base station 10, and the mobile stations are in a CELL_FACH state. The base station 10 is assumed to be connected to an upper network apparatus 30. It should be noted that for designating an arbitrary mobile station, it will be designated as “mobile station 20” hereinbelow.
FIG. 2 is a channel schematic diagram showing a relationship in E-RACH between a preamble, AICH or AICH and E-AICH (which will be designated as AICH/E-AICH hereinbelow), and E-DCH; and FIG. 3 is a sequence chart of channel settings for E-RACH and others. As shown in FIG. 2, in an uplink communication, there are an uplink data channel E-DCH (Enhanced Dedicated Channel), and a preamble for coordinating timing of transmission before transmitting E-DCH. In a downlink communication, there are a downlink channel AICH (Acquisition Indicator Channel) for responding to the preamble received from the mobile station, and E-AICH (Extended AICH) for allocating an E-DCH resource configuration, where AICH and E-AICH are transmitted with the same channelization code for each cell. It should be noted that some base stations do not support E-AICH. In a case that a base station does not support E-AICH and transmission with a default E-DCH resource configuration cannot be achieved, a mobile station performs transmission of the preamble again after a predetermined period of time. As used herein, the term ‘default’ refers to an E-DCH resource configuration index corresponding to a preamble signature.
The preamble employs a preamble signature Csig,s, and a spread code referred to as preamble scrambling code Sr-pre,n, which will be described below. The preamble signature Csig,s is composed of 4096 chips in which an Hadamard code having a code length of sixteen is repeated 256 times, and the preamble scrambling code Sr-pre,n is a cell identification code emitted by a base station. A preamble signature Csig,s is randomly selected by each mobile station from predetermined preamble signatures (Csig,1, Csig,2, . . . , Csig,$), where n designates the index of a scrambling code.
A k-th value of preamble code data Cpre,n,s is constructed from a corresponding k-th preamble signature Csig,s from among 4096 chips and a corresponding preamble scrambling code Sr-pre,n, and is given by EQ. (1) as follows:
                    [                  Equation          ⁢                                          ⁢          1                ]                                                                                  C                          pre              ,              n              ,              s                                ⁡                      (            k            )                          =                                            S                                                r                  -                  pre                                ,                n                                      ⁡                          (              k              )                                ×                                    C                              sig                ,                s                                      ⁡                          (              k              )                                ×                      e                          f              ⁡                              (                                                      π                    4                                    +                                                            π                      2                                        ⁢                    k                                                  )                                                                        (        1        )            
where
k=0, 1, 2, 3, . . . , 4095,
Cpre,n,s: preamble code data,
Sr-pre,n: a preamble scrambling code, and
Csig,s: a preamble signature.
An uplink data channel E-DCH is composed based on a specification stipulated in 3GPP Release 6 (see Non-patent Document 6, for example).
An overview of the operation of E-RACH is shown in FIGS. 2 and 3. The base station 10 periodically broadcasts an E-DCH resource configuration list including an E-DCH resource configuration for use in E-RACH and a corresponding E-DCH resource configuration index, a preamble signature list including preamble signature numbers available in E-RACH, and the aforementioned preamble scrambling code, to mobile stations within the cell using BCH (Broadcast Channel).
The E-DCH resource configuration is comprised of E-RNTI (Enhanced Radio Network Temporary Identity), E-AICH Configuration Flag, Uplink DPCH (Dedicated Physical Channel) Info, E-DCH Info, E-AGCH (E-DCH Absolute Grant Channel) Info, E-RGCH (E-DCH Relative Grant Channel) Info, E-HICH (E-DCH Hybrid ARQ indicator Channel) Info, Downlink F-DPCH Info, TTI, E-DCH Start Time, and the like.
The mobile station 20 transmits preamble code data to the base station with an initial transmit power value calculated from the amount of receive power in a pilot channel of the base station 10. The preamble code data is generated using the preamble scrambling code emitted by the base station 10 and a preamble signature randomly selected by the mobile station. The base station 10 transmits a responsive notification (ACK/NACK) for the received preamble using the AICH signature state to the mobile station 20. In a case that the mobile station cannot use the default E-DCH resource configuration because, for example, another mobile station uses it, the base station 10 that supports E-AICH sends a responsive notification using AICH, and information representing the E-DCH resource configuration to the mobile station using E-AICH.
For example, in a case that the base station 10 has successfully received the preamble transmitted by the mobile station, and allows uplink data to be transmitted using a default E-DCH resource configuration allocated for each preamble signature contained in the preamble, the base station 10 sends a responsive notification ACK using AICH.
On the other hand, in a case that the base station 10 does not allow uplink data to be transmitted using the default E-DCH resource configuration, it sends a responsive notification NACK using AICH. Moreover, for a base station that supports E-AICH, in a case that the base station does not allow uplink data to be transmitted using the default E-DCH resource configuration but allows the uplink data to be transmitted using a non-default E-DCH resource configuration, it sends an offset value indicating an E-DCH resource configuration index allowed to be used to the mobile station using E-AICH according to a method which will be described later.
In a case that uplink data is not allowed to be transmitted even using a non-default E-DCH resource configuration, the base station sends a responsive notification NACK using AICH to the mobile station. Information indicating whether or not the base station supports E-AICH is broadcast to mobile stations within the cell using E-AICH Configuration Flag included in BCH.
In a case that the mobile station 20 has received a responsive notification using AICH, and the response for the preamble signature used in transmission of the preamble is ACK, the mobile station 20 determines an E-DCH transmission profile from a default E-DCH resource configuration allocated to the transmitted preamble signature and the initial transmit power value for the E-DCH calculated from the transmit power value for the transmitted preamble, and transmits the data to the base station 10.
The mobile station can know whether the base station supports E-AICH from E-AICH Configuration Flag mentioned above. In a case that the base station supports E-AICH, and a response to the preamble signature used in transmission of the preamble is NACK, the mobile station receives E-AICH. On the other hand, in a case that the base station does not support E-AICH, and a response to the preamble signature used in transmission of the preamble is NACK, the mobile station transmits the preamble again after a predetermined period of time. In a case that no response to the preamble signature used in transmission of the preamble is received, the mobile station 20 decides that the preamble transmitted before is not received by the base station 10, and unless the upper limit of the number of retransmissions is reached, it retransmits the preamble with a transmit power increased by a predetermined amount. In a case that E-AICH is received and the responsive notification for E-AICH is not NACK, an E-DCH transmission profile is determined from an E-DCH resource configuration corresponding to an offset value obtained from the E-AICH signature number and the E-AICH signature state included in E-AICH, and the data is transmitted to the base station 10. In a case that the responsive notification is NACK, transmission of the preamble is performed again after a predetermined period of time.
It should be noted that, as shown in FIG. 2, a minimum preamble retransmission interval tip-p,min, and an interval τp-a from a preamble to transmission of a responsive notification in AICH are predetermined. For a preamble signature corresponding to a preamble that cannot be recognized by the base station because, for example, the preamble cannot be received at the base station although it was transmitted by the mobile station, no response is made from the base station to the mobile station. In a case that no response is made until τp-a, the mobile station retransmits the preamble.
AICH transmits a responsive notification (ACK/NACK) using the AICH signature state corresponding to the preamble signature Csig,s of the preamble. AICH is composed by combining 32 codes ‘aj’ derived from EQ. (2) below, and the signature pattern bs,j for AICH is defined in Table 1 (see Non-patent Document 4, for example), where s designates an AICH signature number, and bs,j may take sixteen patterns. Moreover, AIs indicates the AICH signature state, which takes AIs=+1 when the responsive notification for AICH is ACK, or AIs=−1 when it is NACK.
                    [                  Equation          ⁢                                          ⁢          2                ]                                                                      a          j                =                              ∑                          s              =              0                        15                    ⁢                                    AI              s                        ⁢                          b                              s                ,                j                                                                        (        2        )            
TABLE 1sbs, 0, bs, 1 . . . , bs, 31011111111111111111111−1−111−1−111−1−111−1−1121111−1−1−1−11111−1−1−1−11311−1−1−1−11111−1−1−1−1111411111111−1−1−1−1−1−1−1−11511−1−111−1−1−1−111−1−111161111−1−1−1−1−1−1−1−111111711−1−1−1−111−1−11111−1−1181111111111111111−1911−1−111−1−111−1−111−1−1−1101111−1−1−1−11111−1−1−1−1−11111−1−1−1−11111−1−1−1−111−11211111111−1−1−1−1−1−1−1−1−11311−1−111−1−1−1−111−1−111−1141111−1−1−1−1−1−1−1−11111−11511−1−1−1−111−1−11111−1−1−1sbs, 0, bs, 1 . . . , bs, 31011111111111111111−1−111−1−111−1−111−1−12111−1−1−1−11111−1−1−1−131−1−1−1−11111−1−1−1−11141111111−1−1−1−1−1−1−1−151−1−111−1−1−1−111−1−1116111−1−1−1−1−1−1−1−1111171−1−1−1−111−1−11111−1−18−1−1−1−1−1−1−1−1−1−1−1−1−1−1−19−111−1−111−1−111−1−11110−1−1−11111−1−1−1−1111111−11111−1−1−1−11111−1−112−1−1−1−1−1−1−11111111113−111−1−11111−1−111−1−114−1−1−111111111−1−1−1−115−11111−1−111−1−1−1−111
E-AICH is composed by combining 32 codes ‘aj’ derived from EQ. (3) below using the same channelization code as that for AICH. The E-AICH signature pattern cs,j is defined in Table 2 (see Non-patent Document 7, for example), where s′ designates an E-AICH signature number, and cs,j may take sixteen patterns at maximum. Moreover, EAIs' designates the E-AICH signature state, and the state of only one E-AICH signature is used per access slot among one or more E-AICH signature numbers to send the offset value to the mobile station.
Table 3 is a table representing an example of correspondence between an E-AICH signature state, an E-AICH signature number, and an offset value indicating an E-DCH resource configuration index. X designates a default E-DCH resource configuration index corresponding to a preamble signature, Y designates the total number of E-DCH resource configurations. The offset value in Table 3 indicates an offset from the E-DCH resource configuration index allocated by default in the E-DCH resource configuration list. For example, when the E-AICH signature state is +1 and the E-AICH signature number is zero, the offset from the E-DCH resource configuration index allocated by default is one. When E-AICH is decoded to obtain an offset of one, the mobile station performs data transmission using an E-DCH resource configuration corresponding to the E-DCH resource configuration index obtained by adding one to the E-DCH resource configuration index allocated by default.
On receipt of E-AICH, the mobile station decodes E-AICH using the E-AICH signature pattern. Decoding of E-AICH may be achieved in a manner in which the E-AICH signature is arranged in order, such as in the order of the E-AICH signature starting from #0, for example, and the E-AICH signature is determined in partial decoding, or in a manner in which after all E-AICH signatures are decoded, an E-AICH signature estimated to have the highest probability is determined. An offset value is determined from the E-AICH signature number obtained by decoding E-AICH, and the E-AICH signature state. An E-DCH resource configuration corresponding to an E-DCH resource configuration index designated by the default E-DCH resource configuration index and obtained offset is used to determine an E-DCH transmission profile.[Equation 3]aj=EAIs′cs′,j  (3)
TABLE 2signatureResourceEAIs′s′configuration index+10NACK−1(X + 1) mod Y+11(X + 2) mod Y−1(X + 3) mod Y+12(X + 4) mod Y−1(X + 5) mod Y+13(X + 6) mod Y−1(X + 7) mod Y+14(X + 8) mod Y−1(X + 9) mod Y+15(X + 10) mod Y−1(X + 11) mod Y+16(X + 12) mod Y−1(X + 13) mod Y+17(X + 14) mod Y−1(X + 15) mod Y+18(X + 16) mod Y−1(X + 17) mod Y+19(X + 18) mod Y−1(X + 19) mod Y+110(X + 20) mod Y−1(X + 21) mod Y+111(X + 22) mod Y−1(X + 23) mod Y+112(X + 24) mod Y−1(X + 25) mod Y+113(X + 26) mod Y−1(X + 27) mod Y+114(X + 28) mod Y−1(X + 29) mod Y+115(X + 30) mod Y−1(X + 31) mod Y
TABLE 3scs, 0, cs, 1 . . . , cs, 3101−11−11−11−11−11−11−11−1111−1−111−1−111−1−111−1−11121−11−1−11−111−11−1−11−11131−1−11−111−11−1−11−111−1141−11−11−11−1−11−11−11−11151−1−111−1−11−111−1−111−1161−11−1−11−11−11−111−11−1171−1−11−111−1−111−11−1−11181−11−11−11−11−11−11−11−1−191−1−111−1−111−1−111−1−11−1101−11−1−11−111−11−1−11−11−1111−1−11−111−11−1−11−111−1−1121−11−11−11−1−11−11−11−11−1131−1−111−1−11−111−1−111−1−1141−11−1−11−11−11−111−11−1−1151−1−11−111−1−111−11−1−11−1scs, 0, cs, 1 . . . , cs, 310−11−11−11−11−11−11−11−11−1−111−1−111−1−111−1−112−11−1−11−111−11−1−11−113−1−11−111−11−1−11−111−14−11−11−11−1−11−11−11−115−1−111−1−11−111−1−111−16−11−1−11−11−11−111−11−17−1−11−111−1−111−11−1−1181−11−11−11−11−11−11−11911−1−111−1−111−1−111−1101−111−11−1−11−111−11−11111−11−1−11−111−11−1−11121−11−11−111−11−11−11−11311−1−111−11−1−111−1−11141−111−11−11−11−1−11−111511−11−1−111−1−11−111−1    Non-patent Document 1: 3GPP TS25.214 v7.5.0, May 2007    Non-patent Document 2: 3GPP TS25.321 v7.2.0, September 2006    Non-patent Document 3: 3GPP TS25.331 v7.3.0, December 2006    Non-patent Document 4: 3GPP TS25.211 v7.2.0, May 2007    Non-patent Document 5: 3GPP RP-070677, Nokia Siemens Networks, Nokia, Ericsson, Qualcomm, T-Mobile, Telecom Italia, “Enhanced Uplink for CELL_FACH State in FDD,” September 2007    Non-patent Document 6: 3GPP TS25.319 v7.3.0    Non-patent Document 7: 3GPP R1-080835, Qualcomm Europe, Ericsson, Nokia, Nokia Siemens Networks, Motorola, “25214CRdraft (Rel-8, B), RACH procedure relation to Enhanced Uplink for CELL_FACH state,” January 2008